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Catalysts based on gold nanoclusters supported by different materials have been used for the selective semihydrogenation of phenylacetylene to styrene. The most active species were formed by catalyst thermal activation in a reductive atmosphere. It is shown that the activity and selectivity of these catalysts is mainly controlled by the interaction of the gold nanoclusters with the support, as demonstrated by using materials with high surface area and different acidity/basicity, i.e. MgO, Al 2 O 3 and Mg/Al hydrotalcite. There is an important influence of the acid/base properties of the support on the selectivity. Higher activity is obtained for gold supported on basic materials (MgO and hydrotalcite) and the best results are obtained with the Au catalyst supported on the MgAl hydrotalcite exhibiting high activity and the best selectivity to the alkene. This was explained by the intermediate basicity of the support that favors the heterolytic cleavage of H 2 while avoiding the overreduction of the alkynes to alkanes. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • ITQ2 supported AgAu nanoclusters are active catalysts for CO oxidation. • AgAu alloyed sites are the most active centres as they favour reactants adsorption. • Different catalyst pretreatments result in different rearrangement of the AgAu atoms. • Nanoclusters evolve during reaction forming active and stable catalytic sites. • Catalytic tests with in situ characterization provides insight into catalyst dynamics. The bimetallic nanocluster catalyst structure can change during pretreatment and reaction, thus in situ characterization techniques are required for a proper analysis of the active sites. In situ XAFS and DRIFTS were used to study the dynamic evolution of the metal active sites in bimetallic Ag x Au 25-x nanoclusters supported on ITQ2 zeolite during CO catalytic oxidation. The activity of the bimetallic nanocluster catalyst in this reaction was significantly higher than those of supported monometallic Ag 25 and Au 25 nanoclusters. These results were explained by the formation of AgAu alloyed nanoparticles, which favoured reactant adsorption and reaction. Furthermore, the initial activity depended on the catalyst pretreatment, obtaining better conversion, at lower temperatures, with the catalyst pretreated with hydrogen than with the catalyst pretreated with oxygen. This was also associated with an easier formation of a AgAu alloy under hydrogen pretreatment at 150 °C. However, the alloying process seemed to be completed after reaction in both cases, i.e. for the catalyst pretreated with oxygen and with hydrogen, obtaining the same catalytic performance with both catalysts upon reuse. The activity is constant in successive reaction runs, indicating high stability of the active species formed under reaction conditions. The results have shown that the combination of catalytic studies with in situ characterization techniques provides insight into the structural dynamics of the catalysts during activation and reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • ITQ2 supported AgAu nanoclusters are active catalysts for CO oxidation. • AgAu alloyed sites are the most active centres as they favour reactants adsorption. • Different catalyst pretreatments result in different rearrangement of the AgAu atoms. • Nanoclusters evolve during reaction forming active and stable catalytic sites. • Catalytic tests with in situ characterization provides insight into catalyst dynamics. The bimetallic nanocluster catalyst structure can change during pretreatment and reaction, thus in situ characterization techniques are required for a proper analysis of the active sites. In situ XAFS and DRIFTS were used to study the dynamic evolution of the metal active sites in bimetallic Ag x Au 25-x nanoclusters supported on ITQ2 zeolite during CO catalytic oxidation. The activity of the bimetallic nanocluster catalyst in this reaction was significantly higher than those of supported monometallic Ag 25 and Au 25 nanoclusters. These results were explained by the formation of AgAu alloyed nanoparticles, which favoured reactant adsorption and reaction. Furthermore, the initial activity depended on the catalyst pretreatment, obtaining better conversion, at lower temperatures, with the catalyst pretreated with hydrogen than with the catalyst pretreated with oxygen. This was also associated with an easier formation of a AgAu alloy under hydrogen pretreatment at 150 °C. However, the alloying process seemed to be completed after reaction in both cases, i.e. for the catalyst pretreated with oxygen and with hydrogen, obtaining the same catalytic performance with both catalysts upon reuse. The activity is constant in successive reaction runs, indicating high stability of the active species formed under reaction conditions. The results have shown that the combination of catalytic studies with in situ characterization techniques provides insight into the structural dynamics of the catalysts during activation and reaction. [ABSTRACT FROM AUTHOR]

• CO oxidation is a test reaction to evaluate the nature and evolution of Ag-species. • The active sites for CO oxidation are the metallic silver species. • Ag-species formed in Ag-ITQ2 depend on the preparation method and the pretreatment. • Ag-nanoclusters evolve during the CO oxidation reaction towards silver nanoparticles. Silver containing zeolites are widely used in heterogeneous catalysis and their catalytic performance is strongly dependent on the nature of the metal species supported on the zeolites. In this work, Ag-ITQ2 zeolites have been prepared by different methods: incipient wetness impregnation, ion exchange and preformed Ag-nanoclusters supported on the zeolite. The samples have been pretreated with oxygen or hydrogen previously to the catalytic test in the CO oxidation reaction. The results allow to correlate the nature of the Ag-species with its catalytic activity in this reaction as metallic silver is active for the CO oxidation but cationic silver does not show significant activity. It is shown that Ag0 is formed on the catalysts prepared by impregnation even without a reduction treatment. On the contrary, Ag-nanoclusters form stable partially charged silver species that only can be reduced to Ag0 nanoparticles under severe thermal conditions. Silver species formed in the catalysts prepared by ion exchange also present a partial positive charge. We concluded that this reaction is a useful test for monitoring the nature and evolution of silver species in the zeolite and to determine the stability of the silver nanoclusters. [ABSTRACT FROM AUTHOR]